Fate of nitrogen in soils planted to soybean crops
Chiu, C.Y.; Yoshida, T.
Soil Science and Plant Nutrition 32(2): 273-284
ISSN/ISBN: 0038-0768 DOI: 10.1080/00380768.1986.10557504
Investigations on the fate of fertilizer nitrogen in the soil-plant ecosystem were carried out. Soyabean plants (nodulating A62-1 and non-nodulating A62-2 cv.) were grown under greenhouse conditions in Light Colored Andosol and Yellow Soil. Tagged ammonium sulfate, enriched to 20.6 atom % 15N was applied as N fertilizer to pots, with and without plants, at the rate of 100 mg N/pot (100 kg N/ha). Fertilizer N recovered by the plants was 67.4% for the nodulating cv. and 62.4% for the non-nodulating cv. in the Andosol and 50.5 and 49.4%, resp., in the Yellow Soil. The unaccounted fertilizer N in the soil-plant system was 18.6 and 22.8% for the nodulating and the non-nodulating cv. in the Andosol and 26.5% in the unplanted soil; in the Yellow Soil 30.2 and 31.1% were not recovered in the nodulating and non-nodulating cv., resp., while the unplanted soil gave a value of 21.2%. Soyabean plants grown in the Andosol derived 21, 27 and 50% of the total plant N from fertilizer, soil and air, resp., while the corresponding values in the plants grown in Yellow Soil were 29, 48 and 23%, resp. Both the fraction of atmospheric N in plant N and the amount of N2 fixed were higher in the Andosol than in the Yellow Soil due to the presence of efficient indigenous Rhizobium populations. To estimate the degree of N fixation, results obtained by the N balance method were in good agreement with those obtained by the isotope dilution method, while the acetylene reduction method gave an underestimation of N fixation.